How to update a 2D array in state?

Question

React

Array like:

Trying to update:

this.setState(prevState => {
            return {
                arr: {
                    ...prevState.arr,
                    [posX]: [
                        ...prevState.arr[posX],
                        [posY] = 1
                    ]
                }
            }
        })

or make it easier

const arr = [...this.state.arr];

        arr[posX][posY] = 1;

        this.setState({
            arr: arr
        })

Answer 1

return {
  arr: {

If arr is an array, why are you trying to turn it into an object?

this.setState(({ arr }) => ({
  arr: arr.map((n, i) => i === posX
    ? n.map((m, j) => j === posY ? 1 : m)
    : n
  ),
}));